In general, the telephone line and power line cables, when the lines have a certain power, they have sufficient diameter so that on a clear day, these may be seen by the birds flying in the zone; however, this visibility is lost easily on cloudy days. Furthermore, normally, there is a neutral cable which, for purposes of safety, extends above the three cables which constitute the electrical phases and which normally have a smaller section than the latter; thus, from one side it is more difficult to see, and from the other side in the terrain, they are usually separated sufficiently from the phase cables because they weigh considerably more, thus adopting a more arched and closer configuration to the soil; therefore, centering in the view of the phase cables it is easy not to notice the existence of this fourth cable above the previous ones and, sometimes, quite a distance away. Needless to say that if this problem is transferred to the helicopters that may fly over the area, or even airplanes, the consequential loss of visibility and resulting collision against the cable would be serious.
Presently there are very few beacons with respect to the same and consequently they are more readily visible; there is also another type of beacon formed by a kind of fixed ball set on the cable by any method; in any of the cases, the beacon shows externally a glossy color, or it is even reflectant, visible from very far away.
The problem posed by these types of beacons is that they require handling by a technician for its installation. If it is installed without turning off power, the risk of possible loads discharged is very high for a worker and of course it is not assumable; to turn off the power supply on certain lines is an extremely costly operation and also it can only be done on certain days a week or a year, with prior notice to the users or the adoption of proper measures of bypassing power supply. To install these types of beacons, a trolley is mounted on the line and a worker climbs on top of it; the cable in question must support both the worker's and the trolley's weight, which we assume to-be about 150 kilograms in the best-case scenario. Furthermore, we must take into account that this cable, since it is on top of the others, is subjected to power load discharges which continuously occur on the lines; therefore, it may be damaged at a given time or point of its travel and consequently it may not support the aforementioned weight at a given point in time; also, it is usually located on the top of a optical fiber cable which obviously does not withstand the tensional stress on a conventional metal cable, and said tensional stresses may affect the proper operation of the fiber. Finally, the worker not only runs some very high risks in the installation of this type of beacons, but also the installation of said beacons may cause the rupture or functional damage of the cable that will support them.